The present invention relates to an information recording and reproducing technique for recording or reproducing data onto or from an optical disk, and more particularly to a technique for controlling laser beam power emitted from a semiconductor laser during recording of the disk.
One way of recording information onto an optical disk is to irradiate the disk with a laser beam when recording a datum representing information xe2x80x9c1xe2x80x9d and not to irradiate the disk with the laser beam when recording a datum representing information xe2x80x9c0xe2x80x9d, i.e. by so called on/off control.
In recent years, however, optical disk recording and reproducing techniques permitting data recording and reproduction at higher densities have become required. Techniques known as one beam overwriting, and write strategy (by which the current waveform used for driving the laser) is pulse-divided to provide multi-value levels to control the recording power of the laser have become indispensable. Especially where overwriting is done, or data are recorded by switching a plurality of power levels to accomplish waveform control for high density mark formation, a plurality of amperages must be switched. In doing so, the laser power at each level must be accurately controlled.
Because each semiconductor laser has its own temperature characteristic, it is usually necessary to control the drive current provided to the laser according to the temperature. One well known method for such control is automatic power control (APC). Conventional APC techniques include, for example, the technique in Japanese Patent Laid-open Publication No. Hei 6-338073. In this example, part of the laser beam emitted by the semiconductor laser is detected with a photodiode, and the detected current is converted with a current-voltage conversion circuit, provided to an amplifier, converted by analog-to-digital (A/D) conversion, and provided to a controller.
This prior art technique, because it uses a configuration in which APC control is accomplished by a controller, makes recording or reproduction of data onto and from an optical disk difficult. Thus, recently, the need for high density mark formation complicats the waveform control of the laser drive current, entailing an increase in the number of laser power levels and finer pulse division, and also necessitating high speed switching of a large number of laser power levels. Because the controller and the laser drive section are relatively distant from each other in a conventional laser drive apparatus, high speed switching of current are susceptible to timing delay, increasing the risk of distortion of the data to be recorded on the optical disk.
In APC operation, the laser power is monitored and corrected by the controller which is distant from the laser drive section, and is therefore susceptible to noise and a consequent risk of erroneous operation. Furthermore, the number of conducting lines connecting the laser drive section and the controller increases, making it difficult to efficiently utilize the mounting space.
The present invention provides a laser drive unit capable of recording/reproduction at high accuracy, even on an optical disk for high density recording. It also provides an information recording and reproducing apparatus mounted with that laser drive unit.
According to a preferred aspect of the invention, a system comprising a waveform controller receives information for a desired laser drive setting from an external controller. The controller provides a laser drive waveform on the basis of that information and at an indicated amperage. The system also includes a current setting unit for setting a laser drive current to match the indicated amperage; a current output unit for adjusting the laser drive current to the laser drive waveform and supplying the adjusted output to a laser diode; and a current setting corrector. The corrector monitors the laser beam emission from the laser diode and corrects the laser drive current set by the current setting unit. The result is precise adjustment of the laser diode power. Preferably, the laser drive waveform controller, current setting unit, current output unit and current setting corrector are formed as a single integrated circuit, or at least on a common substrate.
This configuration, in which the laser drive waveform controller, current setting unit, current output unit and current setting corrector are formed on the same substrate, allows these constituent elements to be in mutually close positions, thus reducing timing lags in laser drive current, and reducing distortion of the data waveform. As a result, data is recorded and reproduced with high accuracy even on high density recording optical disks.
According to another aspect of the invention, a system comprises a laser drive waveform controller, into which information for laser drive setting is entered from an external controller. The system generates a laser drive waveform on the basis of that information and supplies an indicated amperage. It also includes a current setting unit for setting the laser drive current to match the indicated amperage; and a current output unit for adjusting the laser drive current with the laser drive waveform and supplying the adjusted output to a laser diode. Finally, it includes a current setting corrector for monitoring the laser beam emission from the laser diode and correcting the laser drive current set by the current setting unit by digitally processing the monitored signal to adjust the amperage, thereby adjusting the laser diode power. As before, the laser drive waveform controller, current setting unit, current output unit and current setting corrector are preferably formed on the same chip or substrate. This configuration minimizes timing lags, reduces distortion of the data waveform, and makes possible recording and reproduction of data with high accuracy to or from even high density recording optical disk.